WebGL UnityLoader error in Firefox

[monark]

So in Unity 5.6 the UnityLoader.js generates a myCanvas is null error in Firefox. See attached.
I’ve reported a bug but heard nothing as of yet.
I had a quick look at UnityLoader.js but it’s hellish. Does anyone know how to edit it to remove this issue?

After clicking ok the game does load and display as normal. And it doesn’t show this error if opened in a normal browser tab, the issue only appears when opened in it’s own window, which used to be fine in Unity 4.6

[sumpfkraut]

If you use a jslib plugin check the id names there. pearhaps this html element don’t exist.

[monark]

Seems like that console error was a red herring. And the issue lay elsewhere